On Mon, 4 Oct 1999, R Scherer wrote:
> what is active and passive ftp?
A simple way of looking at ftp sessions is based on who sets the ports. A
port number plus a process number is the way packets sent from one IP
address get to the proper place on another IP address.
The most common way to hold an ftp session is for the server to be
"active." That is, it defines the port on which it and a specific client
will communicate. Normally this works just fine. However, if the client is
behind a firewall, that firewall may be configured to reject all packets
except those in response to requests originating from within the firewall.
Obviously, if the ftp server sends packets with a port number unknown to
the firewall, they get rerouted to the bit bucket. The solution is to set
the ftp client software to use "passive" mode. This means that the server
"passively" accepts whatever port number is offered by the client. Since
packets with that port number as part of their address originate within the
firewall, responding packets are allowed back in.
An oversimplified explanation, but it makes the major point of the
differences.
Rich
Dr. Richard B. Shepard, President
Applied Ecosystem Services, Inc. (TM)
Making environmentally-responsible mining happen. (SM)
--------------------------------
2404 SW 22nd Street | Troutdale, OR 97060-1247 | U.S.A.
+ 1 503-667-4517 (voice) | + 1 503-667-8863 (fax) | [EMAIL PROTECTED]
